Doug Kerr
June 1st, 2006, 07:04 PM
The two major families of sensor array used in digital still cameras are the CCD and CMOS types. These two designations actually describe different aspects of the two designs. CCD (charge-coupled device) refers to the ingenious method used to sequentially "shift out" the charge accumulated by the individual pixel photodetectors so these values can be measured and digitized with common circuitry and delivered in a handy way for further processing. Of course, a certain type of "device" construction, produced by a certain fabrication process, is implied.
CMOS refers to the fact that these sensors use the same device construction, and can be fabricated by the same process, as the familiar CMOS integrated circuit chips. But in addition these sensors use a wholly different concept of reading out and digitizing the individual pixel photodetector outputs than the CCD sensors.
The particular architecture and operation used in the type of CMOS sensor we most often encounter is called the "APS" form. No, that doesn't mean "Advanced Photo System", not does it refer to the clumsy convention for denoting a certain general range of digital camera sensor sizes. [Just playing with you!] Rather, it stands for "active pixel sensor". This refers to the fact that each photodetector proper is accompanied by its own supporting squad of transistors (typically three of them) which control the detection process and implement this pixel's role in the ingenious readout scheme.
I have just released to my technical information site, "The Pumpkin", a new tutorial article, "The CMOS APS Digital Camera Sensor", which can be found here:
http://doug.kerr.home.att.net/pumpkin/index.htm#CMOS-APS
It describes the principles, organization, and operation of an illustrative form of the CMOS APS sensor. Basic electrical engineering and semiconductor concepts are encountered, but there are numerous tutorial explanations to assist the reader.
CMOS refers to the fact that these sensors use the same device construction, and can be fabricated by the same process, as the familiar CMOS integrated circuit chips. But in addition these sensors use a wholly different concept of reading out and digitizing the individual pixel photodetector outputs than the CCD sensors.
The particular architecture and operation used in the type of CMOS sensor we most often encounter is called the "APS" form. No, that doesn't mean "Advanced Photo System", not does it refer to the clumsy convention for denoting a certain general range of digital camera sensor sizes. [Just playing with you!] Rather, it stands for "active pixel sensor". This refers to the fact that each photodetector proper is accompanied by its own supporting squad of transistors (typically three of them) which control the detection process and implement this pixel's role in the ingenious readout scheme.
I have just released to my technical information site, "The Pumpkin", a new tutorial article, "The CMOS APS Digital Camera Sensor", which can be found here:
http://doug.kerr.home.att.net/pumpkin/index.htm#CMOS-APS
It describes the principles, organization, and operation of an illustrative form of the CMOS APS sensor. Basic electrical engineering and semiconductor concepts are encountered, but there are numerous tutorial explanations to assist the reader.